The present invention relates to processing digital documents.
A digital document is a collection of digital data that includes digital content for which a presentation structure is defined. The presentation structure is a structure that is used to arrange different portions of the digital content when the document is presented in a user interface. For the content portions, the presentation structure can specify a layout, a sequential, parallel or other ordering, a visual appearance or an audio presentation. The digital content can represent text, graphics, animation, video, audio or any other data carrying information. The content of the document can be digitally signed by adding a digital signature to the document. The digital signature is based on cryptographic techniques and is used to authenticate the signer and the content that has been signed. The authentication verifies the identity of the signer and whether the content is changed since the document has been signed. Optionally, the authentication can also verify whether the signer's digital identity certification has been revoked. Thus the digital signature can have different statuses depending on the state of failure or success to authenticate the signer or the content.
Digital signatures are typically used to sign entire messages that are electronically transmitted, for example, by electronic mail (“e-mail”). If an e-mail message is digitally signed, the recipient can identify the sender and verify if the message was corrupted during the transmission. In a user interface, document management applications typically display the status of a digital signature separate from the content of the document. For example, some e-mail applications indicate the status of the signature in a header that is defined to provide information about the e-mail message. The user interface can also display a control panel that includes menu items or control icons that can be selected by a user for information about the digital signature. In the control panel, the menu items or the icons may include text or symbols that indicate whether a document is digitally signed, and if signed, what is a current status for the digital signature.
Adobe® Acrobat® applications, available from Adobe Systems Incorporated of San Jose, Calif., allow users to embed a graphical representation of the digital signature into the layout defined by a document in Portable Document Format (“PDF”). The signature's representation can include an image illustrating a hand-written signature of the signer or any other image or symbol. Thus similar to traditional paper documents, the signer's signature becomes part of the visual representation of the document, and the location of the signature visually associates the signature with the signed content. To indicate a status of the digital signature, the signature's graphical representation has been changed in the PDF document by the Acrobat® application. For example, a green check mark has been added to the signature's representation to indicate that the signature is valid.